The Apparent Contradiction

Let's go back to our three lab example and now let's imagine that the scientist are trying to measure the speed of light. Before we explain our example let's take into consideration the Law of Propagation. The Law says that the speed the light travel's remains constant at all times, regardless of the motion state of the light-emitter body.

Going back to our example, let's determine that the trailer S has a speed V and that S' has a speed of V'. To measure the speed of light each scientist flashes a lantern from the back of the laboratory (or trailer) to the front. The scientist in the stationary laboratory (S0) succesfully determins c=300000[km/s]. The scientist in S0 communicates his result to the other two scientists. Applying the theorem of addition of velocities the scientis in S' now determins that the speed of light relative to S' will be called w and that  w = c - v and the scientist S' determins that w'=c-v'. In this case the speed of light would've been proved not to be a constat. Whoops!! What happened? We're forced either to disregard the theorem of addition of velocities or the law of propagation and the principle of relativity.

Usually we would say that we should disregard the law of propagation and the principle of relativity, beacuse it seems more logical. However, the studies of electrodynamical and optical phenomena lead to believe that the law of propagation is necesary, the Michelson - Morley Experimen is a good example of that. This makes us disregard the theorem of addition of velocities and the ground is set for Einstein's Special Theory.

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